On-site stormwater management


On-site stormwater management devices provide:

  • water quality treatment with final disposal to surface water or to ground soakage and/or infiltration
  • peak flow and quantity reduction for sites, where final disposal is to surface water

On-site management devices are an important part of any water-sensitive design. Water-sensitive designs protect and incorporate natural site features. These designs consider erosion and sediment control and feature into stormwater management plans. Property owners and developers can manage stormwater discharge and protect the environment by using water sensitive design concepts and features.

Some examples of on-site stormwater management devices are as shown below:


For some new subdivisions and older houses, roof water is discharged to the ground through soak pits. A soak pit is a covered, porous-walled chamber or rock-filled pit that allows water to slowly soak into the ground. The efficiency of a soak pit depends on the permeability of the surrounding ground and the size of the installed pit. Continued maintenance is required for soakage systems, as silting up of the soakage media may occur over time.

The size of the soak pit needs to be calculated for right of ways, parking areas and driveways. Some of these specific designs may need a pre-entry sump.

Flood risk analysis and overland flow designs will need to be assessed for all soak pit designs. When assessing flood risk and overland flow, no allowance for soakage capacity can be assumed.

Retention tanks:

  • collect stormwater from hardstanding areas
  • hold it during the storm, and
  • release it back into the stormwater network at a slower rate.

This helps reduce the pressure on stormwater drainage systems through peak runoff times.

Rain tanks

Rain tanks store rain water for later use, reducing the reliance on mains water use. This provides for economic or environmental benefits, and aids in self-sufficiency.

Soakage trenches

A soakage trench along the edges of paving or driveways, can help and aid stormwater dispersal into the surrounding ground, as long as there is good soakage.

Rain gardens

Create rain gardens in areas with good soakage; like volcanic soils. These aid in capturing and detaining stormwater, and slowly let it soak away into the surrounding ground. Rain gardens filter out pollutants and contaminants in the stormwater. The soil particles and plant roots collect and retain the chemicals, before they reach any streams and coastal environments.

Living roof

Similar to rain gardens, but they are grown on a roof, thus improving both insulation and stormwater management outcomes.

Permeable surfaces

Using permeable paving for paths and driveways can reduce the amount of stormwater that has to be managed. This is because they absorb stormwater into the surrounding ground.

Last updated: 06 Nov 2019